Ionomer-like structure in mature oil paint binding media

Abstract

We use ATR-FTIR and SAXS to demonstrate that oil paint binding media go through an ionomer-like state during ageing.

Time‐Dependent ATR‐FTIR Spectroscopic Studies on Fatty Acid Diffusion and the Formation of Metal Soaps in Oil Paint Model Systems

“…Both these paint models showed broad COO À bands in FTIR spectra that are nearly identical in both shape and intensity to Znpol and Pbpol systems ( Supporting Information, Figure S6), indicating the formation of ionomeric binding media. [8] Figure 4c shows the crystalline MPa 2 profiles for ZnO-LO and Pb 3 O 4 -LO during exposure to HPa solution. Thepigmented films showed very fast MPa 2 crystallization on short timescales.T he concentration of ZnPa 2 in the ZnO-LO system reached ac onstant level after approximately 600 minutes,w hile the concentration of PbPa 2 was still increasing in the Pbpol system after 1000 minutes.…”

“…[6] An important discovery has been that metal ions (originating from pigments or driers) migrate into the binding medium, where they are distributed throughout the polymerized oil network and associated to carboxylate groups. [7][8][9] Such an ionomer medium contains clusters of metal carboxylate groups (identified by abroad n a COO À band in infrared (IR) spectra) that, while potentially reactive towards longchain saturated fatty acids (SFAs), could contribute to the stability of the oil network on the short term. [8] SFAs can either be formed by partial hydrolysis of the polymerized oil network, or be derived from paint additives such as aluminum stearate.…”

“…[7][8][9] Such an ionomer medium contains clusters of metal carboxylate groups (identified by abroad n a COO À band in infrared (IR) spectra) that, while potentially reactive towards longchain saturated fatty acids (SFAs), could contribute to the stability of the oil network on the short term. [8] SFAs can either be formed by partial hydrolysis of the polymerized oil network, or be derived from paint additives such as aluminum stearate. [10] Our current hypothesis,i llustrated in Figure 1, is that the presence of free SFAs leads to the formation of amorphous metal soap complexes.Subsequently,owing to the low solubility of metal soaps in oil, [11] these complexes will tend to crystallize and form metal-soap aggregates.W ith FTIR spectroscopy,this crystalline state of metal soaps can be distinguished from amorphous metal carboxylate species by their sharp COO À bands at 1510 cm À1 (Pb) or 1538 cm À1 (Zn).Linseed oil-based ionomer model systems and timedependent ATR-FTIR spectroscopy were used to investigate the diffusion of aS FA (palmitic acid) and its reaction with metal carboxylate clusters.A TR-FTIR spectroscopy has proven to be ap owerful tool to study dynamic processes in polymer films.…”

“…systems are representative of mature oil paint in terms of metal carboxylate concentration and structure. [7][8][9] We subjected our paint models either to fatty acid in solution or to molten fatty acids,because long-chain fatty acids are solids at room temperature.B oth conditions entail ad eparture from the real conditions in oil paintings to some degree but do allow the studying of essential reaction-diffusion processes.…”

Time‐Dependent ATR‐FTIR Spectroscopic Studies on Fatty Acid Diffusion and the Formation of Metal Soaps in Oil Paint Model Systems

“…An important discovery has been that metal ions (originating from pigments or driers) migrate into the binding medium, where they are distributed throughout the polymerized oil network and associated to carboxylate groups . Such an ionomer medium contains clusters of metal carboxylate groups (identified by a broad ν a COO − band in infrared (IR) spectra) that, while potentially reactive towards long‐chain saturated fatty acids (SFAs), could contribute to the stability of the oil network on the short term .…”